This chapter is from the book

This chapter is from the book

This chapter shows you how to use an important programming
constructarrays. The variables that we looked at in the previous chapters
are scalar variables, which store a single value. An array is a
variable that stores a set or sequence of values. One array can have many
elements. Each element can hold a single value, such as text or numbers, or
another array. An array containing other arrays is known as a multidimensional
array.

PHP supports both numerically indexed and associative arrays. You will
probably be familiar with numerically indexed arrays if you've used any
programming language, but unless you use PHP or Perl, you might not have seen
associative arrays before. Associative arrays let you use more useful values as
the index. Rather than each element having a numeric index, they can have words
or other meaningful information.

We will continue developing the Bob's Auto parts example using arrays to
work more easily with repetitive information such as customer orders. Likewise,
we will write shorter, tidier code to do some of the things we did with files in
the previous chapter.

Key topics covered in this chapter include

Numerically indexed arrays

Associative arrays

Multidimensional arrays

Sorting arrays

What Is an Array?

We looked at scalar variables in Chapter 1, "PHP Crash Course." A
scalar variable is a named location in which to store a value; similarly, an
array is a named place to store a set of values, thereby allowing you to
group scalars.

Bob's product list will be the array for our example. In Figure 3.1, you
can see a list of three products stored in an array format and one variable,
called $products, which stores the three values. (We'll look at
how to create a variable like this in a minute.)

After we have the information as an array, we can do a number of useful
things with it. Using the looping constructs from Chapter 1, we can save work by
performing the same actions on each value in the array. The whole set of
information can be moved around as a single unit. This way, with a single line
of code, all the values can be passed to a function. For example, we might want
to sort the products alphabetically. To achieve this, we could pass the entire
array to PHP's sort() function.

The values stored in an array are called the array elements. Each
array element has an associated index (also called a key) that is
used to access the element.

Arrays in most programming languages have numericalindexes that
typically start from zero or one. PHP supports this type of array.

PHP also supports associative arrays, which will be familiar to Perl
programmers. Associative arrays can have almost anything as the array indices,
but typically use strings.